1. Field of the Invention
The present invention relates to an oil storage method and more particularly, to an underwater oil storage method, which keeps the oil tank under the water in a water pool so that the water in the water pool supports the pressure of the oil tank and isolates storage oil from the ground earth by means of the physical characteristic that the specific gravity of oil is lower than water.
2. Description of the Related Art
An oil storage tank may be mounted above or under the ground. When building an oil tank above the ground, a strong floor construction must be built up on the ground. The floor construction must be strong enough to support the heavy cylindrical or spherical steel shell of the oil tank and the oil stored in the oil tank. A conventional oil tank uses a steel shell to bear the pressure of the oil stored therein. The capacity has a limitation. Further, increasing the capacity of an oil tank will relatively increase the cost. For safety's sake, a retaining wall must be built around the oil tank(s) such that when oil leaks out of the oil tank(s), leaked oil can still be kept within the retaining wall to prevent contamination or any possible catastrophe. At present time, the capacity of Formosa Petrochemical Corp.'s oil tank is 130,000 square meters (the largest oil tank in Asia Pacific area. This oil tank has a diameter about 86 meters and a height about 24 meters. The steel shell of the oil tank must strong enough to bear the pressure of 24M-depth storage oil and to provide a damping resistance against earthquake grade 6. It took about 2 years to finish the construction of the oil tank after finish of the ground construction. The total cost for this oil tank is about two hundred millions NT dollars. Because this oil tank is exposed to the weather, it must be regularly maintained to remove rust and regularly painted. In case of a leakage of oil, the storage oil must be fully discharged out of the oil tank and cleaned so that a soldering process can be employed to seal the crevice. Maintaining this oil tank is a hard and expensive task.
Further, when directly building an oil tank under the ground, the cost is high. In case of a leakage occurred, it is difficult to detect such a leakage, and leaked oil will permeate into the soil to pollute underground water.